1. Field of the Invention
The present invention relates to the technical field of a liquid ejecting device for use in an ink jet recording head or the like to eject ink droplets or other droplets and, in particular, to a liquid ejecting device with long service life capable of preventing nozzle plugging due to ink precipitation or the like over a long period of time and to an ink jet printer utilizing this liquid ejecting device as the ink jet recording head.
2. Description of the Related Art
A thermal ink jet which rapidly vaporizes a portion of ink through heating with a heater and causes ink droplets to be ejected through a nozzle by its expanding force, etc. is utilized in various printers (See JP 48-9622 A, JP 54-51837 A, etc.).
In another known printer, an oscillation plate is caused to oscillate by a driving device, such as an MEM (micro electronic machine) utilizing static electricity or a piezoelectric element, and ink droplets are ejected through a nozzle by its energy (See JP 11-207956 A, JP 11-309850 A, etc.).
In such an ink jet printer, during storage, for example, when the printer is turned off, leaving the ink jet recording head (hereinafter referred to as the recording head) unattended causes water or other solvent of ink to vaporize, which gives rise to coagulation and precipitation of the solid content (solute) of ink such as dye or pigment, resulting in nozzle plugging (clogging). The clogging of the nozzle leads to a reduction (fluctuation) in the ink ejection amount until the ejection of ink becomes impossible. As a result, the printer cannot function as it should.
In view of this, in an ordinary ink jet printer, capping (sealing) is effected on the nozzle during storage, thereby preventing nozzle plugging. FIG. 9 schematically shows an example of such conventional arrangement.
In the example shown in FIG. 9, when driving the printer (turning it on), a cap 152 for covering the nozzle is spaced apart from a recording head 150 (head unit) so that it may not hinder image recording.
When the printer is turned off, the surface of the recording head 150 in which the nozzles are formed (A large number of nozzles are arranged perpendicular to the plane of the drawing) (hereinafter referred to as the nozzle surface 150a) is cleaned by a wiper or the like (not shown), and then the cap 152 is moved to the recording head 150 side to hermetically cover the nozzle surface 150a, effecting capping on all the nozzles. In many cases, the cap 152 is connected to a suction device, which sucks the interior of the cap 152 as needed after covering the nozzle surface 150a, thereby making it possible to effect capping more reliably.
In the capping of the nozzle of such a recording head 150, equilibrium is reached when the interior of the cap 152 attains saturation vapor pressure. Thereafter, the portion around the nozzles is stabilized, making it possible to prevent nozzle plugging due to ink precipitation or the like.
However, when the capping by the cap 152 is incomplete or when some ink remains around the nozzles as a result of frequent repetition of small amounts of printing, the ink is allowed to gradually vaporize/precipitate around the nozzles, with the result that the nozzles become clogged.
The present invention has been made with a view toward solving the above problem in the prior art. It is an object of the present invention to provide a liquid ejecting device capable of satisfactorily preventing nozzle plugging due to ink precipitation or the like during storage and little affecting the ink droplet ejection from the nozzles even if ink precipitates during storage, thus realizing an ink jet recording head or the like having a long service life. Another object of the present invention is to provide an ink jet printer utilizing this liquid ejecting device.
In order to attain the object described above, the first present invention provides a liquid ejecting device comprising: a member in which a plurality of nozzles are formed; a plurality of ejecting units each of which is formed in correspondence with each of the plurality of nozzles and ejects a liquid droplet from each of the plurality of nozzles; and a plurality of supply passages each of which supplies liquid to each of the plurality of ejecting units, wherein a first liquid level position for a driving period and a second liquid level position for a storage period which are different from each other are set in each of a plurality of liquid flow passages comprising each of the plurality of nozzles and each of the plurality of supply passages corresponding to the each of the plurality of nozzles.
Preferably, the first and second liquid level positions for the driving and storage periods are adjusted by a pressure adjustor for adjusting a pressure of the liquid.
Preferably, a contact angle at which the liquid comes in contact with an inner wall surface of one of the plurality of liquid flow passages at the first liquid level position for the driving period is different from a contact angle formed at the second liquid level position for the storage period.
Preferably, each of the plurality of liquid flow passages has a larger section size at the second liquid level position for the storage period than at the first liquid level position for the driving period.
Preferably, the second liquid level position for the storage period is set downstream from the first liquid level position for the driving period in a direction in which the liquid is ejected.
Preferably, a groove extending in the direction in which the liquid is ejected is formed in an inner wall surface of each of the plurality of liquid flow passages between the first liquid level position for the driving period and the second liquid level position for the storage period.
Preferably, the liquid is supplied during the storage period through each of the plurality of supply passages or a separately provided liquid supply unit or both of them.
Preferably, the pressure adjustor is provided between a liquid tank to the plurality of supply passages.
Preferably, the liquid is ink, the liquid droplet is an ink droplet, and the liquid ejecting device is an ink jet recording head.
In order to attain the object described above, the second aspect of the present invention provides an ink jet printer having an ink droplet ejecting device as an ink jet recording head, the ink droplet ejecting device comprising: a member in which a plurality of nozzles are formed; a plurality of ejecting units each of which is formed in correspondence with each of the plurality of nozzles and ejects an ink droplet from each of the plurality of nozzles; and a plurality of supply passages each of which supplies ink to each of the plurality of ejecting units, wherein a first ink level position for a driving period and a second ink level position for a storage period which are different from each other are set in each of a plurality of ink flow passages comprising each of the plurality of nozzles and each of the plurality of supply passages corresponding to the each of the plurality of nozzles.
Preferably, the first and second ink level positions for the driving and storage periods are adjusted by a pressure adjustor for adjusting a pressure of the ink.
Preferably, a contact angle at which the ink comes in contact with an inner wall surface of one of the plurality of ink flow passages at the first ink level position for the driving period is different from a contact angle formed at the second ink level position for the storage period.
Preferably, each of the plurality of ink flow passages has a larger section size at the second ink level position for the storage period than at the first ink level position for the driving period.
Preferably, the second ink level position for the storage period is set downstream from the first ink level position for the driving period in a direction in which the ink is ejected.
Preferably, a groove extending in the direction in which the ink is ejected is formed in an inner wall surface of each of the plurality of ink flow passages between the first ink level position for the driving period and the second ink level position for the storage period.
Preferably, the ink is supplied during the storage period through each of the plurality of supply passages or a separately provided ink supply unit or both of them.
Preferably, the pressure adjustor is provided between an ink tank to the plurality of supply passages.